The object of this experiment is to become familiar with the instruments used in the low noise laboratory.

Transcription

1 0. ORIENTATION 0.1 Object The object of this experiment is to become familiar with the instruments used in the low noise laboratory. 0.2 Parts The following parts are required for this experiment: 1. A solderless breadboard. It can be purchased from the Barnes and Noble Georgia Tech or The Engineers Bookstore. 2. One wire jumper kit. It can be purchased at either bookstore. 0.3 Instruments There are 6 stations in the lab. Each has almost identical equipment. Hewlett-Packard 3400A True RMS AC Voltmeter. Thisisatruermsanalog voltmeter. It correctly measures the rms value of a voltage (assuming that the bandwidth of the signal is less than the bandwidth of the meter). Hewlett-Packard 427A Voltmeter. This is an averaging analog voltmeter. It correctly measures the rms value of sine waves with no dc level. For all other types of signals a correction factor must be used. Hewlett-Packard 3468B DMM. This is a digital rms voltmeter. When set to ac, it correctly measures the rms value of an input signal (assuming that the bandwidth of the signal is much less than that of the meter). Hewlett-Packard 3312A Function Generator. This is an analog function generator that has several modulation features. ORIENTATION 1

2 Hewlett-Packard 33120A Function Generator. Thisisadigitalfunctiongenerator that has numerous programmable features and can be interfaced with a computer. It can also be used to obtain the frequency response of circuits. Hewlett-Packard 6235A Triple DC Power Supply. Thisisabasicdcpower supply that is used to power electronic circuits. Tektronix 2245A Oscilloscope. This is a four channel 100 MHz oscilloscope. It is a smart analog oscilloscope, which means that it has time and voltage cursors as well as the autoset feature. Tektronix 754D Oscilloscope. This is a four channel 500 MHz oscilloscope. It is a digital oscilloscope with a phosphor display. Hewlett-Packard 35665A Dual Channel Dynamic Signal Analyzer. This is a programmable dual input digital spectrum analyzer. It samples the input signal and performs a Fast Fourier Transform on the sampled data. The spectrum is then displayed. Numerous signal processing features such as averaging and peak hold are incorporated into this instrument. It also has a source of white Gaussian noise (source output) which is digitally generated. It is an extended audio spectrum analyzer which evaluates signals in the band from 1 µhz to 100 khz. It is the basic instrument that is used to examine noise spectra. PC. Each station has a dedicated pc that is used to control the digital instruments at that station. Each pc is connected to the internet but is not on a domain. Under no circumstance is the Windows Messanger to be enable or used. In addition to the equipment at each station there are three stand alone instruments: Phillips 6300A RCL Meter. This is a microprocessor based instrument that measures the impedance of a circuit component and determines whether it is a resistor, capacitor, inductor, or neither, and displays the component value. The measurement is made at the frequency of 1 khz. No other measurement frequencies can be used. Hewlett-Packard 4263B LCR Meter. Thisisalsoadigitalmeterusedtomeasure component values. Tektronix 370A Curve Tracer. This is a digital curve tracer used to obtain the terminal characteristics of active devices. TIMS Communications Simulator. This is a modular instrument used to simulate blocks of communications systems. 2 ORIENTATION

3 0.4 Laboratory Procedure Voltage Measurement 1. Turn on the HP 33120A function generator. 2. Set the function generator for High Z. (Shift, Enter, right or left arrow until SYS Menu is found, down arrow, right or left arrow until OUT TERM is found, down arrow,rightorleftuntilhigh Z is found, ENTER). 3. Set the function generator to produce a sine wave with a frequency of 1 khz, a dc level of 0 (default value), and a rms amplitude of 1 V. 4. Turn on the HP 3400 voltmeter, HP 427A voltmeter, and HP 3468B DMM. 5. Measure the ac value of the output voltage of the function generator with each. Note any discrepancy between the readings. 6. Turn on the Tektronix 2245A and Tektronix 754D oscilloscopes. 7. Measure the output voltage of the function generator with each oscilloscope. 8. Turn on the HP 35665A Dynamic Signal Analyzer. 9. Connect the output of the function generator to the Channel 1 input of the Dynamic Signal Analyzer. Nothing should be connected to the other two inputs at this time. 10. Set the Dyanmic Signal Analyzer SPAN to 10 khz (Freq, SPAN, 10kHz). 11. Use the Dynamic Signal Analyzer to measure the output voltage from the function generator. All of the voltages measurements should be close Resistance and Capacitance Measurement 1. Obtain a 15 kω resistor (5% resistor color code brown green orange) and a 0.01µF capacitor (103k or.01). The printed value is the nominal value of these components. 2. Use the Philips RCL meter and the Hewlett-Packard 4263B LCR meter to measure the actual value of these components. LABORATORY PROCEDURE 3

4 0.4.3 First Order Circuit 1. Use the resistor and capacitor along with the HP 33120A function generator to assemble a first order RC low pass filter. 2. Use the oscilloscopes to determine the 3 db frequency. 3. Exchange the resistor and capacitor to form a first order high pass filter and repeat. 4. Turn off the HP 33120A function generator and remove all leads connected to it. 5. Connect a BNC to BNC jumper from the SOURCE output of the HP 35665A Dynamic Signal Analyzer to the Channel 1 input of the analyzer. 6. Connect the SOURCE output to the input of the low pass filter and Channel 2 to the output of the low pass filter. 7. Set the INSTRUMENT MODE to SWEPT SINE. 8. Set the SOURCE level to 1 V rms. 9. Set the DISPLAY FORMAT to BODE. 10. Press Freq and Sweep Mode to LOG. PressSTART. 11. After the frequency response has been plotted, press PLOT/PRINT, MORE SETUP, and switch the plot dump destination from HPIB to File. 12. Insert a high quality formatted floppy disk into the disk drive of the signal analyzer. 13. Press RETURN and then press START PLOT/PRINT. 14. Remove the floppy disk and use the pc to print it with the software package View Companion. 15. Remove the BNC connector for Channel Noise Signal Analyzer Source 1. Press Preset on the signal analyzer. 2. Connect the SOURCE out to the Channel 1 input. 3. Turn the source on and set it to random noise with a level of 1 V rms. 4. Press Trace Coordinates and set it to log. 4 ORIENTATION

5 5. Observe the spectra. Is it reasonably white? 6. Turn the averaging on and use the default number of averages of Position the cursor to the middle of the screen and record the voltage level indicated as V db. 8. Press Disp Format and then Measurement State. 9. Record the measurement bandwidth f, BW (it is a function of the frequency span). 10. The volts per root hertz of the noise source is then given by v n = 10V db/20 f 11. Press Marker Func, BAND, BAND MARKER, and select the start as 0 Hz and the stop and 115 khz. 12. Press BAND POWER. The value indicated should be close to the value of 1 V rms which in decibels is 0 db. 13. Measure the source output with the three voltmeters and record the values. 14. Connect the source output to the Channel 1 input of the signal analyzer. 15. Press Instrument Mode, Histogram, Measurement Data and select CDF. 16. Print the display. Select pdf and print the display. 17. Connect the source output to the Channel 1 input of the oscilloscopes. 18. Adjust the volts per division to 1 V per division for both oscilloscopes. 19. Switch the digital oscilloscope from storage to non storage and note the difference between the displays. 20. Use the Tektronix software Wavestar to print the display that appears on the digital oscilloscope. 21. Remove the connection from the SOURCE output on the signal analyzer to the Channel 1 input Noise Function Generator Source 1. Connect the output of the HP33120A function generator to the Channel 1 input on the signal analyzer. Select noise as the output and set the level to 1 V rms. Repeat the above noise measurements. LABORATORY PROCEDURE 5

6 0.4.6 Noise Arbitrary Waveform Generator 1. Open Mathcad. Use the following code to import the white noise data. Programming HP33120A Function Gen for Noise Output D := Insert Component. Input table. Import data. N := last( D) i:= 0.. N 1 d := D i i Max := max( d) Min := min( d) Define vector to be table entry. Normalize Data for Function Generator from -1 to + 1 Max + Min d := d i i 2 2 Max Min Type "d=" put pointer into displayed vector, right click, select all copy selection. Paste into Intuitlink. After the data has been pasted from Mathcad to Intuilink, export the data to the HP33120A Function/Arbitrary Waveform Generator. Repeat the noise measurements. 2. Repeat the above for the pink noise data. 3. Turn off the HP33120A and remove all leads connected to it Noise TIMS Noise Source 1. Connect the Noise Source on the TIMS Communications Simulator to the TIMS voltmeter with a banana plug to banana plug connector. Adjust the noise level until it is 1 V rms. Repeat the above noise measurements. 6 ORIENTATION

7 0.4.8 Noise Transistor Noise Source 1. Assemble the circuit shown below. Use either a 2N3904 or 2N4401 NPN BJT transistor and a 741 or other op amp. The op amp requires power supply rails of +15 and 15 Volts. Power supply decoupling caps (100 µf electrolytic) and series resistor of 51 Ω (5 %) should be used. The transistor is being operated in its reverse breakdown region for the base-emitter junction and emulates a Zener diode. The output noise level is a function of the dc collector current which can be adjusted with the resistor R 1. The gain of the op amp stage is set by the resistors R 2 and R 3. The components will have to be varied to obtain optimal noise performance. Initially, use: R 1 = 100 kω, R 2 =10kΩ, andr 3 =100kΩ. Use a 51 Ω 5% resistor for R o (this resistor is there for practical reasons and has no effect on the noise performance of the circuit.). The capacitor C is a 10 µf electrolytic. 2. Repeat the above noise measurements on this source Laboratory Report 1. Present the data taken using tables and plots. 2. Compare the pdf and cdf measured for the various noise sources with the theoretical expressions for Gaussian noise with an rms value of 1 V. Which noise source was the best? Which was the worst? 3. What was the largest value of the noise voltage observed with the oscilloscopes? Which source produced it? LABORATORY PROCEDURE 7